 Although carbon fibers are produced using similar process steps, formation of thermoplastic fibers, stabilization, and carbonization, their final structures that govern the end properties may be significantly different. Process parameters have slight effect on microstructure; however, the final structure strongly depends on the starting polymer precursor. Polyacrylonitrile (PAN) and Pitch are the most predominant polymer precursors used in the production of carbon fibers. PAN-based carbon fibers consist of nanocrystalline graphitic domains typically 1.5 � 5 nm in size surrounded by amorphous carbon; instead pitch-based carbon fibers are 10 to 50 nm crystallites where the graphitic (002) planes (d = ~0.334 nm) are mostly aligned parallel to the fiber axis. These fibers typically show a difference in nanostructure between the skin and core of the fiber. It has been seen that the skin-core structure plays significant role on mechanical properties. Design of more homogenous carbon fiber microstructure by controlling the starting polymer and process parameters resulted in different set of tensile strength and elastic modulus properties which has not been observed in skin-core structure PAN carbon fibers. The microstructural defect distribution (0.1nm to 200nm) measured by small angle X-Ray scattering also showed direct relationships with tensile strength of carbon fibers. Therefore, research into understanding the formation of carbon structures from various polymer precursors offers opportunity for designing microstructures leading to improved properties and reduced cost carbon fiber.

Structure and properties of carbon fibers

245th National Meeting (2013)

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